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Biomedical subjects

K Pan

Publications and source records attributed to K Pan.

12 recordsLinked to original sources
PubMed2001

[Grey correlation and cluster analysis on relationship between Cercidiphyllum japonicum community and its environment].

The relationship between 10 years old C. japonicum plantation forest community and its environmental conditions was studied by grey correlation method and cluster analysis. The results showed that there existed closer relations among soil organic matter, available Ca, Fe, Mg and N. Except for N and Mn, all soil available elements tested had no direct impact on the absorption and accumulation of corresponding elements by the community. The tree species in different habitats was found to absorb soil elements selectively to some extent. The factors affecting the basal diameter, DBH, height and biomass of C. japonicum could be lined as soil chemical characteristics > soil physical properties > climate factors, in which, available P had little impact on the growth of C. japonicum. It is suggested that C. japonicum could be restored in the area with higher air moisture and with fertile porous soil between elevation of 2200-2700 m.

Cluster Analysis↗
PubMed2001

[The effect of mouthguard on strength of the musculus deltoideus].

OBJECTIVE: To investigate the effect of mouthguard on strength of musculus deltoideus and to observe the possibility of its improving sports ability. METHODS: The custom mouthguards were fabricated respectively for 8 subjects with soft resin by direct method. The activities of the musculus deltoideus and masseter were tested by means of electromyograph (EMG), while the subjects lay, made maximum voluntary biting with mouthguard and pressed 5 kg. The EMG potentials were transferred to a computer. The data were handled and the integral values of EMG were exported. RESULTS: The subjects set a great value on the mouthguard's comfort, retention and protection. The EMG values of the musculus deltoideus and masseter of the subjects biting with mouthguards were 1.1600 v/s and 0.3825 v/s, and the values of those biting without mouthguards were 0.6125 v/s and 0.213 8 v/s, respectively. The muscular strength of the former was significantly improved compared with that of the latter (P < 0.01). CONCLUSIONS: Wearing a mouthguard and maximum voluntary biting can enhance the masseter force and reflectively improve the musculus deltoideus strength.

Electromyography↗
PubMed2001

[The murine submandibular gland conditioned medium induce the development of CFU-GM and CFU-meg].

OBJECTIVE: Our purpose is to determine whether murine submandibular gland produce hematopoietic growth factors or not and which hematopoietic growth factor are produced by murine submandibular gland. METHODS: By using the techniques of culture of hematopoietic progenitor cells(CFU-GM, CFU-Meg) ex vivo, flow-cytometry, the effects of murine submandibular gland conditioned medium(SGCM) on the development of CFU-GM and CFU-Meg in mice was studied. RESULTS: SGCM can stimulate the development of CFU-GM and CFU-Meg (without any exogeneous HGF), almost no colony in control (without any exogeneous HGF and SGCM); the promoting activity of male SGCM is higher than female SGCM's in augmenting colony formation of CFU-Meg (P < 0.05), there is no difference of CFU-GM(P > 0.05). The stimulating activity of anemic mice SGCM is higher normal mice SGCM's (P < 0.05). IL-3 can collaborate with female SGCM to stimulate proliferation of CFU-Meg. SGCM can promote bone morrow cell entiring the active proliferative phase(S/G2). CONCLUSION: Submandibular gland can stimulate the development of CFU-GM and CFU-Meg by secreting hematopoietic growth factor-like activities. Our study provide the experimental evidences for clarifying the relationship between submandibular gland and hematopoiesis.

Animals↗
PubMed2001

[Effect of human umbilical vein endothelial cells on granulopoiesis, erythropoiesis and megakaryopoiesis in mice].

OBJECTIVE: To investigate the effects of endothelial cells on the proliferations of granulocytic, erythrocytic and megakaryocytic progenitor cells. METHODS: Human umbilical vein endothelial cells were collected within 12 hours after cesarean section and were cultured according to Jaffe's method. The human endothelial culture supernatant (HECS) harvested from primary culture medium was centrifuged. Bone marrow mononuclear cells of mice were prepared and then cultured in semi-solid agar or methylcellulose with the addition of HECS. RESULTS: Colony-forming yields were increased in the culture systems with HECS. But in the systems with no HECS, exogenous GM-CSF, EPO and IL-3 added to the hematopoietic progenitor cultures were necessary to induce colony-forming. Synergistic increase in progenitor cell expansion was observed when both HECS and exogenous cytokines were added to hematopoietic progenitor cultures. CONCLUSION: 1. Endothelial cells can support the proliferation and differentiation of hematopoietic stem and progenitor cells. 2. HECS as a source of standard hematopoietic growth factors can be used in the expansion of stem cells in vitro and in the therapy of hemopathy. 3. Interactions between endothelial cells and hematopoietic stem cell or progenitors may play an important role in the regulation of hematopoiesis in vivo. 4. Endothelial cells may produce other soluble growth factors potentiating the action of a set of cytokines such as GM-CSF and IL-6.

Animals↗
PubMed1998

D,L-S-methyllipoic acid methyl ester, a kinetically viable model for S-protonated lipoic acid as the oxidizing agent in reductive acyl transfers catalyzed by the 2-oxoacid dehydrogenase multienzyme complexes.

D,L-S(6,8)-Methyllipoic acid methyl ester triflate salt (D,L-S-methyllipoic acid methyl ester) was synthesized as a model for S-protonated lipoic acid, suggested to be the active form of lipoic acid in the reductive acylation catalyzed by the E1 and E2 enzymes of the 2-oxoacid dehydrogenase multienzyme complexes by a previous model [Chiu, C. C., Chung, A., Barletta, G., and Jordan, F. (1996) J. Am. Chem. Soc. 118, 11026-11029]. While in that earlier study lipoic acid could only trap only the enamine/C2 alpha-carbanion intermediate in an intramolecular model, and with the assistance of mercury compound to shift the equilibrium to the products, D,L-S-methyllipoic acid methyl ester could trap the enamine derived from 2-alpha-methoxybenzyl-3,4,5-trimethylthiazolium salt in an intermolecular reaction in the absence of a mercury compound, and with a rate constant of 6.6 x 10(4) M-1 S-1. A tetrahedral adduct at the C2 alpha-position formed between the enamine and D,L-S-methyllipoic acid methyl ester was isolated and characterized. The reaction likely takes place by two-electron nucleophilic attack, since no evidence was found for C2 alpha-linked homodimers, expected from a free-radical mechanism. The results suggest that, in the reductive acyl transfer, there is nucleophilic attack by the enamine at one of the sulfur atoms of the lipoic acid [probably at S8, according to Frey, P. A., Flournoy, D. S., Gruys, K., and Yang, Y. S. (1989) Ann. N.Y. Acad. Sci. 373, 21-35], while there is concomitant electrophilic catalysis by a proton juxtaposed at S6 via a general acid catalyst located on the E1 enzyme. Oxidation of the enamine derived from C2 alpha-hydroxybenzyl-3,4,5-trimethylthiazolium salt by D,L-S-methyllipoic acid methyl ester was also deduced on the basis of the formation of 2-benzoylthiazolium ion as a major product; however, the tetrahedral intermediate could not be detected. Oxidation of the enamine by D,L-S-methyllipoic acid methyl ester can take place with either an ether or an alcohol at the C2 alpha position of the enamine.

Acylation↗
PubMed1998

[Studies on infection of Helicobacter pylori and their subtypes cagA+ and hspA+ in population living in the areas with high and low incidence of gastric cancer].

OBJECTIVE: To explore the difference in infection of Helicobacter pylori (Hp) and their subtypes cagA+ and hspA+ in the residents living in the areas with high and low incidence of gastric cancer. METHODS: Immunoglobulin G and A antibodies against Hp and immunoglobulin G antibodies against cagA+ and hspA+ were detected for the residents in Linqu and Cangshan Counties of Shandong Province with enzyme-linked immunosorbent assay (ELISA). RESULTS: Rate of infection with Hp in the residents in Linqu County, an area with high incidence of gastric cancer, was 73.8 percent, significantly higher than that in Cangshan County (59.9%), an area with low incidence. Rates of infection with Hp cagA+ and hspA+ in the residents in Linqu County were 50.9 and 17.0 percent, respectively, also significantly higher than those in Cangshan County (34.0% and 13.2%, respectively). Sensitivities and specificities of the methods for detecting antibodies against Hp, cagA+ and hspA+ were 92.3, 63.2 and 21.9 percent and 71.0, 80.6 and 95.2 percent, respectively, evaluated with 13C-urea breath teat (13C-UBT). Rate of infection with Hp, especially with Hp cagA+, correlated significantly with the high incidence of gastric cancer. CONCLUSION: The methods for detecting antibodies against Hp and cagA+ subtype are more sensitive and can be used as better indicators in epidemiological studies on gastric cancer.

Adult↗
PubMed1996

Preliminary crystallographic studies of a protein from Pachyrrhizus erosus.

Crystals of a protein extracted from the seeds of Pachyrrhizus erosus have been obtained by vapor-phase diffusion. The crystal belongs to the space group P4(1)2(1)2 or P4(3)2(1)2 with cell parameters a = b = 62.52, c = 147.42 A. There is one protein molecule of 33 kDa in an asymmetric unit. A data set at 3.1 A has been collected on an area detector.

Journal Article↗
PubMed1995

[Preliminary studies on microbe-mediated N-nitrosamide synthesis].

Chemical synthesis of N-nitrosamide and influences on it by bacteria and fungi isolated from human gastric juice were studied with trace analysis method to explore the pathway of its endogenous formation. Results showed in synthesis of N-methyl-N-nitrosourea (MNU) with precursors of methylurea (0.42 mmol/L) and sodium nitrite (25 mmol/L) in a condition simulating human stomach, pH of the reaction system played an important role in the synthesis, the amount of synthetic chemical maximized at a pH of 1-3 and almost no synthesis was found at pH of 5-7. A study on the ability to synthesize MNU catalyzed by bacteria isolated from the patients with stomach cancer living in a high-risk area showed its synthesis could be accelerated by Pseudomonas aeruginosa at pH of 6-7 with its catalyzing activity existed in heat liable component of living bacteria. This is the first report showing microorganisms to catalyze the formation of N-nitrosamide from its precursors.

Gastric Juice↗
PubMed1994

Structure of trichosanthin at 1.88 A resolution.

Trichosanthin (TCS) is one of the single chain ribosome-inactivating proteins (RIPs). The crystals of the orthorhombic form of trichosanthin have been obtained from a citrate buffer (pH 5.4) with KCl as the precipitant. The crystal belongs to the space group P2(1)2(1)2(1) with a = 38.31, b = 76.22, c = 79.21 A. The structure was solved by molecular replacement method and refined using the programs XPLOR and PROLSQ to an R-factor of 0.191 for the reflections within the 6-1.88 A resolution range. The bond length and bond angle in the protein molecule have root-mean-square deviations from ideal value of 0.013 A and 3.3 degrees, respectively. The refined model includes 247 residues and 197 water molecules. The TCS molecule consists of two structural domains. The large domain contains six alpha-helices, a six-stranded sheet, and an antiparallel beta-sheet. The small domain has a largest alpha-helix, which shows a distinct bend. The possible active site of the molecule located on the cleft between two domains was proposed. In the active site Arg-163 and Glu-160, Glu-189 and Arg-122 form two ion pairs, Glu-189 and Gln-156 are hydrogen bonded to each other. Three water molecules are bonded to the residues in the active site region. The structures of TCS molecule and ricin A-chain (RTA) superimpose quite well, showing that the structures of the two protein molecules are homologous. Comparison of the structures of the TCS molecule in this orthorhombic crystal with that in the monoclinic crystal indicates that there are no essential differences of the structures between the two protein crystals.

Amino Acid Sequence↗
PubMed1993

Attentional distribution in visual space.

The horizontal extent of the visual attentive field was measured by the use of a two-choice-RT task and compatible and incompatible distractors. The target was a line that inclined either to the left or to the right. Whether or not the subject performed the choice RT was made contingent upon whether two other stimuli presented in the visual display matched or mismatched. The match-mismatch stimuli varied in locations so as to manipulate the relevant visual area (the attended area). The locations of the distractors were also varied. The increase in RT associated with incompatible distractors was found to vary inversely with their distance from the edge of the area attended to and independently of their distance from the target lines. The results were interpreted in terms of an inhibitory field that surrounds the area attended to.

Adult↗
PubMed1993

Attentional distribution in the visual field during same-different judgments as assessed by response competition.

Judgments of same and different on a comparison task have been found to be subject to response competition if an irrelevant stimulus is presented in the display along with the target stimuli. For example, the reaction time for judging two letters the same is markedly increased if a different but irrelevant letter is also present in the display (C. W. Eriksen, O'Hara, & B. [A.] Eriksen, 1982). We have made use of this competition effect to map the visual attentional field in two dimensions. In two experiments, we varied the size of the attended area by varying the separation of the comparison stimuli. The boundaries of the attended area were mapped by varying the location of a response-competitive irrelevant noise letter. On this task, the attended area was found to be elliptical in shape, with the location of the target stimuli defining the major axis. The minor axis of the ellipse increased in direct proportion to increases in the major axis. Rather than interpret these field effects in terms of areas of enhanced processing, we propose that instead they represent the limits or failures in inhibition of competing stimulation.

Adult↗